The present invention relates to a flame-retardant aromatic polyamide resin composition and moldings.
Aromatic polyamide resins are excellent in heat resistance, mechanical properties, molding processability, chemical resistance and the like and are widely used for automotive parts, electric and electronic parts, machine parts, etc. When aromatic polyamide resins are used in these applications, a flame retardant needs to be added to the aromatic polyamide resin in order to impart flame retardancy to the resin for prevention of ignition due to the generation of heat. Especially, when these resins are used for electric and electronic parts, the resins are required to have a flame retardancy as high as V-0 (a level of flame retardancy at which combustion does not continue for longer than a specific period of time and there occurs no dripping of molten resin which ignites cotton) according to UL Standard (Underwriters Laboratories, Inc., Standard for Tests for Flammability of Plastics Materials).
Various flame-retardant aromatic polyamide resin compositions comprising an aromatic polyamide resin and a flame retardant have been proposed and include, for example, a composition comprising an aromatic polyamide resin, brominated polystyrene and antimony oxide (Japanese Unexamined Patent Publications Nos. 263985/1994 and 263986/1994); a composition comprising an aromatic polyamide resin, brominated polystyrene, magnesium hydroxide and the like (Japanese Unexamined Patent Publication No. 196875/1995); a composition comprising an aromatic polyamide resin and a halogen-substituted phosphazene compound (Japanese Unexamined Patent Publications Nos. 133470/1974 and 132149/1974), etc.
However, the halogen compound which is incorporated as the flame retardant into these compositions thermally decomposes during molding of resins, and generates hydrogen halide, unavoidably resulting in corrosion of molds, and in degradation and discoloration of the resin. When resin moldings are burned by a fire or the like, hydrogen halide and the like raise another problem of giving off gases and smoke which are harmful to organisms.
On the other hand, flame-retardant aromatic polyamide resin compositions which do not contain a halogen compound are known and include, for example, a composition comprising an aromatic polyamide resin, an inorganic filler, red phosphorus, melamine cyanurate and the like (Japanese Unexamined Patent Publication No. 161848/1980); a composition comprising an aromatic polyamide resin, a phenolic resin, an aldehyde resin, red phosphorus, a filler and the like (Japanese Unexamined Patent Publications Nos. 25956/1979 and 80357/1979) and so on.
However, these compositions entail a problem that because of red phosphorus present therein, the moldings produced from the composition are inevitably markedly colored and are difficult to use for the above-mentioned purposes. Japanese Unexamined Patent Publication Nos. 183864/1997 discloses a composition comprising an aromatic polyamide resin, a phosphorylamide compound, cyanuric acid and the like. The disclosed composition, although free of both the halogen compound and red phosphorus, gives molded products which are unsatisfactory in flame retardancy and mechanical properties.
Halogen-free phosphate compounds are widely used as a flame retardant for thermoplastic resins. Various flame-retardant resin compositions containing such phosphate compound are proposed. Known as halogen-free phosphate compounds are, for example, resorcinol-bis(diphenyl phosphate), hydroquinone-bis(diphenyl phosphate), bisphenol-A-bis(diphenyl phosphate), bisphenol-S-bis(diphenyl phosphate), resorcinol-bis(dixylyl phosphate), hydroquinone-bis(dixylyl phosphate), bisphenol-A-bis(ditolyl phosphate), bisphenol-A-bis(dixylyl phosphate), bisphenol-S-bis(dixylyl phosphate), etc. However, the resin compositions containing these phosphate compounds can not sufficiently prevent dripping of molten resin when moldings of the composition are burned. Consequently even if these phosphate compounds are incorporated into a resin composition, it is impossible to obtain a flame-retardant composition and moldings which have flame retardancy as high as V-0 in UL Standard.
Furthermore, known as a flame retardant is a crosslinked phosphazene compound (Japanese Unexamined Patent Publication No. 181429/1999) in which at least one phosphazene compound selected from the group consisting of a cyclic phenoxyphosphazene compound represented by the formula (1) 
wherein m is an integer of 3 to 25 and Ph is a phenyl group and a linear phenoxyphosphazene compound represented by the formula (2) 
wherein X1 represents a group xe2x80x94Nxe2x95x90P(OPh)3 or a group xe2x80x94Nxe2x95x90P(O)OPh, Y1 represents a group xe2x80x94P(OPh)4 or a group xe2x80x94P(O)(OPh)2, n is an integer of 3 to 10000 and Ph is as defined above
is/are crosslinked with at least one crosslinking group selected from the class consisting of o-phenylene group, m-phenylene group, p-phenylene group and bisphenylene group represented by the formula (3) 
wherein A is xe2x80x94C(CH3)2xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94 and a is 0 or 1;
wherein
(i) each of the crosslinking groups is interposed between the two oxygen atoms left after the elimination of phenyl groups from the phosphazene compound; and
(ii) the amount of the phenyl groups in the crosslinked compound is 50 to 99.9% based on the total amount of the phenyl groups in the phosphazene compound represented by the formula (1) and/or the phosphazene compound represented by the formula (2). The foregoing crosslinked phosphazene compound has a free hydroxyl group(s) in the molecule. The process for preparing the crosslinked phosphazene compound which is disclosed in Publication No. 181429/1999 gives a crosslinked phosphazene compound in which a hydroxyl group(s) is/are unavoidably left, the hydroxyl group(s) being derived from an alkali metal salt of aromatic dihydroxy compound used as the raw material. The reason therefor is as follows.
According to the research by the present inventors, it was found that the alkali metal salt of aromatic dihydroxy compound shows an exceedingly lower reactivity in a reaction with the dichlorophosphazene compound than the alkali metal salt of phenol. Stated more specifically, when a dichlorophosphazene compound is mixed with an alkali metal salt of phenol with heating, there is produced a phenoxyphosphazene in which the chlorine atom is substituted with a phenoxy group. On the other hand, when a dichlorophosphazene compound is mixed with an alkali metal salt of aromatic dihydroxy compound with heating, substantially no reaction occurs in which the chlorine atom is substituted with a phenoxy group.
Consequently, according to the process disclosed in Japanese Unexamined Patent Publication No. 181429/1999 (in which a dichlorophosphazene compound is reacted with an alkali metal salt of phenol and an alkali metal salt of aromatic dihydroxy compound), a great difficulty is entailed in completely substituting the chlorine atom in the dichlorophosphazene compound with two OM groups (M=alkali metal) of the alkali metal salt of aromatic dihydroxy compound. Accordingly the OM groups remaining unreacted with the chlorine atom are converted into OH groups, with the result that a phenoxyphosphazene compound having a hydroxyl group is produced.
The crosslinked phosphazene compound disclosed in Japanese Unexamined Patent Publication No. 181429/1999 has the following defect as the flame retardant due to free hydroxyl groups in the molecule.
When a resin composition prepared by incorporating the crosslinked phosphazene compound disclosed in Japanese Unexamined Patent Publication No. 181429/1999 into a resin is stored for a prolonged period of time, the moldings molded from the composition exhibit a low flame retardancy and impaired mechanical properties.
An object of the present invention is to provide a flame-retardant aromatic polyamide resin composition which is free of a halogen compound so that no hydrogen halide is generated due to heat decomposition of halogen compound and which would not cause corrosion of molds or degradation and discoloration of the resin.
Another object of the invention is to provide a flame-retardant aromatic polyamide resin composition whose moldings would not give off gases or smoke of halogen halide harmful to organisms when burned in a fire or the like.
A further object of the invention is to provide a flame-retardant aromatic polyamide resin composition and moldings which have excellent flame retardancy corresponding to V-0 in UL Standard.
A still further object of the invention is to provide flame-retardant aromatic polyamide resin moldings which would not drip a molten resin or would prevent dripping of molten resin when the flame-retardant aromatic polyamide resin moldings are burned.
An additional object of the invention is to provide flame-retardant aromatic polyamide resin moldings which the inherent desirable characteristics such as mechanical properties and molding processability possessed by aromatic polyamide resin are not impaired but retained as they are.
A further additional object of the invention is to provide flame-retardant aromatic polyamide resin moldings which are molded from an aromatic polyamide resin composition capable of imparting excellent flame retardancy and mechanical properties to the moldings even when the composition is stored for a long time.
The present inventor conducted extensive research to achieve the foregoing objects and found that the desired flame-retardant aromatic polyamide resin composition can be produced by adding a specific compound shown below in a predetermined proportion to an aromatic polyamide resin. The present invention was completed based on such finding.
According to the invention, there is provided a flame-retardant aromatic polyamide resin composition comprising (a) 100 parts by weight of an aromatic polyamide resin, (b) 0.1 to 100 parts by weight of a crosslinked phosphazene compound, (c) 1 to 60 parts by weight of an inorganic fibrous substance and 1 to 60 parts by weight of magnesium hydroxide, the crosslinked phosphazene compound (b) being at least one phosphazene compound selected from the group consisting of a cyclic phenoxyphosphazene compound represented by the formula (1) 
wherein m is an integer of 3 to 25 and Ph is a phenyl group and a linear phenoxyphosphazene compound represented by the formula (2) 
wherein X1 represents a group xe2x80x94Nxe2x95x90P(OPh)3 or a group xe2x80x94Nxe2x95x90P(O)OPh, Y1 represents a group xe2x80x94P(OPh)4 or a group xe2x80x94P(O)(OPh)2, n is an integer of 3 to 10000 and Ph is as defined above,
said at least one phosphazene compound being crosslinked with at least one crosslinking group selected from the class consisting of o-phenylene group, m-phenylene group, p-phenylene group and bisphenylene group represented by the formula (3) 
wherein A is xe2x80x94C(CH3)2xe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94Sxe2x80x94 or xe2x80x94Oxe2x80x94 and a is 0 or 1;
wherein
(i) each of the crosslinking groups is interposed between the two oxygen atoms left after the elimination of phenyl groups from the phosphazene compound;
(ii) the amount of the phenyl groups in the crosslinked compound is 50 to 99.9% based on the total amount of all phenyl groups in the phenoxyphosphazene compound represented by the formula (1) and/or the phenoxyphosphazene compound represented by the formula (2); and
(iii) the crosslinked phosphazene compound has no free hydroxyl group in the molecule.
According to the invention, there are provided flame-retardant aromatic polyamide resin moldings which can be molded from the foregoing flame-retardant polyamide resin composition.
The flame-retardant aromatic polyamide resin composition of the invention comprises as the essential components an aromatic polyamide resin, a specified crosslinked phosphazene compound, an inorganic fibrous substance and magnesium hydroxide.
Aromatic polyamide resins useful in this invention are not limited insofar as they are those containing in the main chain, as repeating units, a group comprising bivalent residue selected from bivalent aromatic cyclic residues and bivalent heterocyclic residues bonded to amide residue (xe2x80x94CONHxe2x80x94). Any of conventional ones can be used.
Examples of bivalent aromatic residues are phenylene, alkylene phenylene, dialkylene phenylene, biphenylene, a group represented by the formula 
wherein X is alkylene group having 1 to 5 carbon atoms, oxygen atom, sulfur atom, a group xe2x80x94COxe2x80x94 or a group xe2x80x94SO2xe2x80x94, naphthalene group and so on. Examples of bivalent heterocyclic residues are bivalent thiazole residues, bivalent benzoimidazole residues, etc.
One or more groups such as nitro, hydroxy, carboxy and alkoxy may be present as the substituent on the aromatic ring or heterocyclic ring of bivalent residues. The number of these substituents are not limited. For example, phenylene group may have 1 to 4 substituents, biphenylene group 1 to 8 substituents, naphthalene group 1 to 6 substituents, bivalent thiazole residue one substituent, and bivalent benzoimidazole residue have 1 to 4 substituents.
Examples of aromatic polyamide resins containing in the main chain, as repeating units, a group comprising bivalent aromatic cyclic residue bonded to amide residue are polyamide MXD6 resins, modified nylon 6T resins, polyphenylene isophthalamide, polyphenylene terephthalamide, polybenzamide, polyamideimide, polyamide ester, polyamide-hydrazide, polysulfonamide, polyamideimide ester, etc.
Example of the aromatic polyamide resin containing in the main chain, as repeating units, a group comprising bivalent heterocyclic residue bonded to amide residue are polyamidebenzimidazole, polythiazoleamide, etc.
Among these aromatic polyamide resins, it is preferred to use those containing in the main chain, as repeating units, a group comprising bivalent aromatic residue bonded to amide residue. Preferred examples include aromatic polyamide resins containing in the main chain, as repeating units, a group formed by the reaction of terephthalic acid, isophthalic acid or like dibasic acid with a diamine such as hexamethylenediamine, 4,4xe2x80x2-diaminodiphenylmethane, p-phenylenediamine, m-phenylenediamine or the like, or a group formed by the reaction of adipic acid, sebacic acid or like dibasic acids with a diamine such as 4,4xe2x80x2-diaminodiphenylmethane, p-phenylenediamine, m-phenylenediamine or the like.
Aromatic polyamide resins may be those containing, as the bond unit, xe2x80x94COxe2x80x94, xe2x80x94OCOxe2x80x94, xe2x80x94SO2xe2x80x94, xe2x80x94NHxe2x80x94COxe2x80x94COxe2x80x94NHxe2x80x94 and xe2x80x94CH2xe2x80x94 in addition to xe2x80x94CONHxe2x80x94. Preferred aromatic polyamide resins include those containing xe2x80x94CONHxe2x80x94 in an amount of 10 mole % or more of the total of these bond units.
Aromatic polyamide resins to be used in the invention can be easily prepared by the processes disclosed in numerous known publications including, for example, xe2x80x9cTakayuki OHTSU, Masaetsu KINOSHITA; Koubunshi Gosei no Jikkenhou (Methods of Preparing Polymers), Kagaku-Dojin Publishing Co., Ltd., published on Mar. 15, 1988xe2x80x9d, pp.309 to 330; xe2x80x9cJuushukugou to Juufuka (Polycondensation and Polyaddition), edited by editing committee for polymer experimentation by Polymer Society, Kyoritsu Shuppan Co., Ltd. published on Aug. 15, 1980xe2x80x9d, pp. 83 to 103; xe2x80x9c4th Edition, Jikken Kagaku Kouza (Experimental Chemistry Lecture), Vol.28, edited by The Chemical Society of Japan, published by Maruzen Co., Ltd., on May 6, 1992xe2x80x9d, pp.252 to 287; Japanese Examined Patent Publications Nos. 14399/1960, 13247/1960, 10863/1972, 15637/1967, etc.
In the invention, other resins can be mixed with the aromatic polyamide resin. Specific examples of such resins are aliphatic polyamides such as polyamide 6, polyamide 6, 6, polyamide 6, 12, polyamide 4, 6 and the like, polyethylene, polypropylene, polyisoprene, polybutadiene and like polyolefins, modified polyolefin, acrylonitrile-butadiene-styrene resins, acrylonitrile-styrene resins, styrene-maleinic acid copolymers, styrene-maleinic acid-acrylonitrile copolymers, polyphenylene ether, modified polyphenylene ether, polyarylate, polycarbonate, liquid crystal polymer, polytetrafluoroethylene, etc. There is no limitation on the proportions of the aromatic polyamide resin and other resins. The proportions thereof can be properly selected depending on various conditions such as compatibility of the resin with aromatic polyamide resins, the purpose of the resin composition obtained by mixing the resins, etc. Usually the other resin is used in an amount of 200 parts by weight or less, preferably 100 parts by weight or less, more preferably 50 parts by weight or less, per 100 parts by weight of the aromatic polyamide resin.
The crosslinked phosphazene compound of the invention is a compound prepared by crosslinking at least one species of phosphazene compound selected from the group consisting of the cyclic phenoxyphosphazene of the formula (1) and the linear phenoxyphosphazene compound of the formula (2) with at least one species of crosslinking group selected from the class consisting of o-phenylene group, m-phenylene group, p-phenylene group and bisphenylene group of the formula (3),
wherein
(i) each of the crosslinking groups is interposed between the two oxygen atoms left after the elimination of phenyl groups from the phosphazene compound;
(ii) the amount of the phenyl groups in the crosslinked compound is 50 to 99.9% based on the total amount of all phenyl groups in the phosphazene compound represented by the formula (1) and/or phosphazene compound represented by the formula (2); and
(iii) the crosslinked phenoxyphosphazene compound has no free hydroxyl groups in the molecule.
The crosslinked phenoxyphosphazene compound is characterized by the above features (i) to (iii) so that it can give higher flame retardancy to the aromatic polyamide resin than conventional phenoxyphosphzene compounds.
Among the above-mentioned crosslinked phenoxyphosphazene compounds, it is preferred to use the cyclic phenoxyphosphazene of the formula (1) wherein m is 3 to 8 and/or the linear phenoxyphosphazene compound of the formula (2) wherein n is an integer of 1000 to 5000 which is crosslinked with the foregoing crosslinking group represented by the formula (3), wherein a is 1, and A is at least one species selected from the class consisting of a group xe2x80x94C(CH3)2, a group xe2x80x94SO2xe2x80x94 and a group xe2x80x94Sxe2x80x94.
The foregoing crosslinked phenoxyphosphazene compound can be prepared, for example, by reacting at least one species of dichlorophosphazene compound selected from the group consisting of a cyclic dichlorophosphazene represented by the formula (4) 
wherein m is as defined above, and a linear dichlorophosphazene represented by the formula (5) 
wherein X2 represents a group xe2x80x94Nxe2x95x90PCl3 or a group xe2x80x94Nxe2x95x90P(O)Cl, Y2 represents a group xe2x80x94PCl4 or a group xe2x80x94P(O)Cl2 and n is as defined above with a mixture of an alkali metal phenolate represented by the formula (6) 
wherein M is an alkali metal and at least one diphenolate selected from the group consisting of an alkali metal diphenolate represented by the formula (7) 
wherein M is as defined above and an alkali metal diphenolate represented by the formula (8) 
wherein A, a and M are as defined above (first step) and then reacting the above-obtained compound with the foregoing alkali metal phenolate (second step).
The dichlorophosphazene compounds of the formulas (4) and (5) to be used as the raw materials in the foregoing producing process can be produced according to known processes disclosed in, for example, Japanese Unexamined Patent Publication No. 87427/1982, and Japanese Examined Patent Publications Nos. 19604/1983, 1363/1986, and 20124/1987, etc. An example of the processes comprises reacting ammonium chloride and phosphorus pentachloride (or ammonium chloride, phosphorus trichloride and chlorine) at a temperature of about 120 to about 130xc2x0 C. to remove hydrochloric acid.
The alkali metal phenolate represented by the formula (6) can be selected from a wide variety of conventional compounds and includes, for example, sodium phenolate, potassium phenolate, lithium phenolate and the like. These alkali metal phonolates can be used either alone or in combination.
In the alkali metal diphenolate of the formula (7), two OM groups (M is as defined above) may be in any position relation among ortho- , meta- and para- . Specific examples of the foregoing alkali metal diphenolate are alkali metal salts of resorcinol, hydroquinone or catechol and the like. Among them, sodium salt and lithium salt are preferable. The alkali metal diphenolates can be used either alone or in combination.
Examples of the alkali metal diphnenolate of the formula (8) are alkali metal salts of 4,4xe2x80x2-isopropylidene diphenol(bisphenol-A), 4,4xe2x80x2-sulfonyldiphenol(bisphenolxe2x80x94S), 4,4xe2x80x2-thiodiphenol, 4,4xe2x80x2-oxydiphenol or 4,4xe2x80x2-diphenol and the like. Among them, sodium salt and lithium salt are preferable. These alkali metal diphenolates can be used either alone or in combination.
In the invention, the alkali metal diphenolate of the formula (7) and the alkali metal diphenolate of the formula (8) can be used either alone or at least two of them may be used in admixture.
In the first step of the foregoing process, it is desirable to adjust the amounts of the alkali metal phenolate and alkali metal diphenolate to ensure that the chlorine atom in the dichlorophosphazene compound is not completely consumed in the reaction with the alkali metal phenolate and alkali metal diphenolate, namely the chlorine atom in the dichlorophosphazene compound still remains after completion of the reaction with the alkali metal phenolate and alkali metal diphenolate. Thereby the two OM groups (M is as defined above) of the alkali metal diphenolate is bonded to the phosphorus atom of dichlorophosphazene compound. The amounts of the alkali metal phenolate and alkali metal diphenolate used in the first step are such that a total amount of the two compounds is about 0.05 to about 0.9 equivalent, preferably about 0.1 to about 0.8 equivalent, based on the amount of chlorine atom of the dichlorophosphazene compound.
In the second step of the foregoing process, it is desirable to adjust the amount of the alkali metal phenolate to ensure that the chlorine atom in the compound produced in the first step and free hydroxyl groups are completely consumed by the reaction with the alkali metal phenolate. In the present invention, the amount of the alkali metal phenolate to be used is about 1 to about 1.5 equivalents, preferably about 1 to about 1.2 equivalents, based on the amount of chlorine atom of the dichlorophosphazene compound.
In the invention, the proportions of the alkali metal phenolate (combined amounts used in the first and second steps) and alkali metal diphenolate (alkali metal diphenolate/alkali metal phenolate, mole ratio) are in the range of from about 1/2000 to about 1/4, preferably from about 1/20 to about 1/6.
The reactions in the first and second steps are conducted at a temperature ranging from room temperature to about 150xc2x0 C., preferably about 80 to about 140xc2x0 C., and are completed in about 1 to about 12 hours, preferably about 3 to about 7 hours. The reactions in the first and second steps are conducted in an organic solvent such as benzene, toluene, xylene or like aromatic hydrocarbons, monochlorobenzene, dichlorobenzene, and like halogenated aromatic hydrocarbons.
According to the invention, a dichloro-phosphazene compound is reacted with a mixture of alkali metal phenolate and alkali metal diphenolate (first step) and the obtained compound is reacted with an alkali metal phenolate (second step). The above-mentioned specific process gives a crosslinked phenoxyphosphazene compound wherein no free hydroxyl group is left in the molecule, M is removed from the two OM groups of alkali metal diphenolate and the two oxygen atoms are bonded to phosphorus atoms in the dichlororphosphazene compound.
The crosslinked phenoxyphosphazene compound prepared by the foregoing reaction can be easily isolated and purified from the reaction mixture by usual isolation methods such as washing, filtration, drying or the like.
The crosslinked phenoxyphosphazene compound has a decomposition temperature in the range of 250 to 400xc2x0 C.
The amount of the phenyl groups in the crosslinked phenoxyphosphazene compound is 50 to 99.9%, preferably 70 to 90%, based on the total amount of the phenyl groups in the cyclic phenoxyphosphazene compound represented by the formula (1) and/or chain-like phenoxyphosphazene compound represented by the formula (2).
In the formula (2), terminal groups X1 and Y1 may vary depending on the reaction conditions. When the reaction is carried out under ordinary conditions, e.g. when a mild reaction is conducted in a nonaqueous system, the compound has a structure wherein X1 is xe2x80x94Nxe2x95x90P(OPh)3 and Y1 is xe2x80x94P(OPh)4. If the reaction is performed under such a condition that moisture or an alkali metal hydroxide is present in the reaction system or under a severe condition such that a rearrangement reaction takes place, the compound having a structure wherein X1 is xe2x80x94Nxe2x95x90P(O)OPh, and Y1 is xe2x80x94P(O)(OPh)2 exists as mixed with the above compound.
The resin composition of the invention contains the phosphazene compound in an amount of 0.1 to 100 parts by weight, preferably 1 to 40 parts by weight, per 100 parts by weight of the aromatic polyamide resin. If the amount is less than 0.1 part by weight, the phosphazene compound may fail to give the aromatic polyamide resin flame retardancy corresponding to V-0 in UL Standard. On the other hand, if more than 100 parts by weight is used, the flame retardancy is not enhanced and deteriorated mechanical properties may be imparted to the moldings.
Inorganic fibrous substances to be used in the invention are not limited insofar as they are inorganic materials in the form of fibers, and such substances include a wide variety of conventional ones. Specific examples of useful inorganic fibrous substances are fibrous alkali metal titanate, fibrous transition metal borate, fibrous alkaline earth metal borate, fibrous zinc oxide (Japanese Examined Patent Publications Nos. 5529/1985 and 51657/1991, etc.), fibrous titanium oxide, fibrous magnesium oxide (Japanese Unexamined Patent Publications Nos. 11223/1985 and 210000/1986, etc.), fibrous gypsum (Japanese Examined Patent Publications Nos. 12235/1983 and 34410/1983, etc.), fibrous aluminum silicate (Japanese Examined Patent Publications Nos. 76956/1992 and 96480/1995, etc.), fibrous calcium silicate (Japanese Unexamined Patent Publications Nos. 319199/1996 and 40840/1997, etc.), fibrous silicon carbide (Japanese Unexamined Patent Publication No. 109811/1981, Japanese Examined Patent Publication No. 4999/1989, etc.), fibrous titanium carbide (Japanese Examined Patent Publication Nos. 45638/1984 and Japanese Unexamined Patent Publication No. 250225/1987, etc.), fibrous silicon nitride (Japanese Unexamined Patent Publication Nos. 17499/1982 and 17500/1982), fibrous titanium nitride (Japanese Unexamined Patent Publications Nos. 221198/1990 and 173000/1995), carbon fibers, alumina fibers, alumina-silica fibers, zirconia fibers, glass fibers, quartz fibers, etc.
Among these inorganic fibrous substances, it is desirable to use those having a shape anisotropy. Examples of such inorganic fibrous substances are fibrous alkali metal titanate, fibrous transition metal borate, fibrous alkaline earth metal borate, fibrous zinc oxide, fibrous titanium oxide, fibrous magnesium oxide, fibrous gypsum, fibrous aluminum silicate, fibrous calcium silicate, fibrous silicon carbide, fibrous titanium carbide, fibrous silicon nitride, fibrous titanium nitride and like inorganic fibrous substances having a shape anisotropy. Among them, particularly preferred are fibrous alkali metal titanate, fibrous transition metal borate, fibrous alkaline earth metal borate, fibrous titanium oxide, fibrous calcium silicate and like inorganic fibrous substances having a shape anisotropy. Among these inorganic fibrous substances, it is especially desirable to use those having an average fiber diameter of about 0.05 to about 2.0 xcexcm, an average fiber length of about 1 to about 500 xcexcm, and an aspect ratio (fiber length/fiber diameter) of 5 or more, preferably 10 or more.
Among these inorganic fibrous substances, it is preferred to use an inorganic fibrous substance having a pH of 6.0 to 9.5. The pH of the inorganic fibrous substance referred to herein is a pH value as determined at 20xc2x0 C. after stirring a suspension of 1.0 wt. % of inorganic fibrous substance (in deionized water) for 10 minutes. If the pH is significantly more than 9.5, this may deteriorate the properties of aromatic polyamide resin and may lower resistance to heat discoloration. Hence it is undesirable. On the other hand, a pH of far below 6.0 not only reduces the effect of enhancing the strength of the obtained resin composition, but also is responsible for corrosion of processing machine and mold which would occur due to the remaining acid.
These inorganic fibrous substances can be used either alone or in combination.
The amount of the inorganic fibrous substance in the composition of the invention is 1 to 60 parts by weight, preferably 5 to 40 parts by weight, per 100 parts by weight of the aromatic polyamide resin. If less than 1 part by weight is used, the effect of preventing dripping of molten resin is unsatisfactory, whereas more than 60 parts by weight decreases the relative concentration of the phosphazene compound serving as the flame retardant, decreasing the flame retardancy of the obtained resin composition.
In the invention, magnesium hydroxide prevents dripping of molten resin due to the synergistic effect achieved by its combined use with the crosslinked phosphazene compound and the inorganic fibrous substance when the resin moldings are burned.
The magnesium hydroxide to be used herein can be any of commercial products and synthesized products. Preferred magnesium hydroxide is one which contains 0.01 to 1 wt % of volatiles when heated at 120xc2x0 C. for 1 hour and which has an average particle size of 0.1 to 100 xcexcm, and a specific surface area (BET (Brunauer-Emmett-Teller) method) of 0.1 to 500 m2/g. Among these magnesium hydroxide compounds, more preferred are those which contain 0.05 to 0.5 wt % of the foregoing volatiles and which has an average particle size of 0.5 to 30 xcexcm, and a specific surface area of 1 to 20 m2/g. The average particle size was measured by CAPA-300 (Horiba/Nature centrifugal sedimentation type automatic particle size distribution measuring device, product of Horiba Seisakusho Co., Ltd.). If the volatile content is less than 0.01 wt. %, magnesium oxide is produced as a by-product, resulting in a likelihood of reducing the flame retardancy. On the other hand, if the volatile content markedly exceeds 1 wt. %, the volatiles may decrease the mechanical properties of the resin in kneading the resin with magnesium hydroxide. When the average particle size is less than 0.1 xcexcm, or when the specific surface area is less than 0.1 m2/g, it is difficult to handle the magnesium hydroxide. When the average particle size is more than 100 xcexcm, or when the specific surface area is more than 500 m2/g, it is difficult to fully disperse the components in kneading the resin with magnesium hydroxide, making it difficult to give sufficient flame retardancy to the obtained composition.
The magnesium hydroxide particles may be coated with fatty acid, fatty acid salt, silicon compound, epoxy compound or the like. Examples of the fatty acid are laurie acid, myristic acid, palmitic acid, stearic acid, etc. Examples of the fatty acid salt are salts of the above-exemplified fatty acid with sodium, potassium, magnesium, calcium, barium or like alkali metals or alkaline earth metals. Examples of the silicon compound are vinyl tris(xcex2-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, xcex3-(methacryloyloxypropyl)trimethoxysilane, xcex3-aminopropyltriethoxysilane, etc. Examples of the epoxy compound are xcex2-(3,4-epoxycyclohexyl)ethyltrimethylsilane, xcex3-glycidoxypropyltrimethoxysilane, etc.
The magnesium hydroxide particles can be coated by conventional methods. For example, the fatty acid or the like is dissolved in an organic solvent such as methanol, isopropyl alcohol, acetone or the like. Then, magnesium hydroxide is added to the solution, and the mixture is stirred, mixed, filtered, washed and dried in a hot air dryer. The magnesium hydroxide particles may be either partly or entirely coated, but preferably entirely coated.
The magnesium hydroxide for use herein are commercially available under the trade names xe2x80x9cKISUMA 120, 5A, 5B, 5E, and 5Jxe2x80x9d from Kyowa Kagaku Kogyo Co., Ltd.), and under the trade names xe2x80x9cMagnesium Hydroxide 1, 2A and 2Bxe2x80x9d from Umai Kasei Kogyo Co., Ltd., etc.
The amount of magnesium hydroxide in the resin composition of the invention is 1 to 60 parts by weight, preferably about 5 to 40 parts by weight, per 100 parts by weight of the aromatic polyamide resin. The use of magnesium hydroxide in an amount of less than 1 part by weight produces insufficient effect of preventing dripping of molten resin when the resin molding is burned. If the amount is more than 60 parts by weight, the mechanical properties of the resin moldings are decreased.
The flame-retardant aromatic polyamide resin composition of the present invention may contain inorganic fillers conventionally used in the field of flame-retardant resins within the range which does not impair the preferred characteristics. Examples of such inorganic fillers are aluminum hydroxide, magnesium sulfate, calcium sulfate, barium sulfate, aluminum sulfate, aluminum ammonium sulfate, aluminum potassium sulfate, aluminum sodium sulfate, magnesium carbonate, calcium carbonate, aluminum phosphate, ammonium phosphate, etc. These inorganic fillers can be used either alone or in combination.
Additionally, the flame-retardant aromatic polyamide resin composition of the present invention may contain various additives (other than inorganic fillers) conventionally used in the field of flame-retardant resins within the range which does not decrease the preferred characteristics. Examples of such additives are flame retardants other than crosslinked phosphazene compounds, UV absorbers, light stabilizers, antioxidants, light screens, metal deactivators, light quencher, heat resistance stabilizers, lubricants, mold releasing agents, coloring agents, antistatic agents, antiaging agents, plasticizers, impact strength improving agents, other fillers than the above fillers and compatibilizers. These additives can be used either alone or in combination.
The flame-retardant aromatic polyamide resin composition of the invention can be prepared by mixing or kneading the above-mentioned essential components and optionally other additives according to conventional processes. For example, an aromatic polyamide resin is melted by a single-screw extruder, a twin-screw extruder or like extruders, Banbury mixer, a pressure kneader, or a twin-roll kneader or like kneaders, and a crosslinked phosphazene compound, an inorganic fibrous substance, magnesium hydroxide, and optionally other additives are added and kneaded. Alternatively, the aromatic polyamide resin, an inorganic fibrous substance, magnesium hydroxide and optionally other additives are dry-blended, and the obtained mixture is mixed and melted by the extruder, the kneader or the like, and to the mixture a crosslinked phosphazene compound is added and kneaded.
The flame-retardant aromatic polyamide resin composition of the invention can be molded into flame-retardant resin moldings. For example, the resin composition can be molded into resin plates, sheets, films, special shape products or like moldings of various shapes by, for example, injection molding, extrusion molding (including sheet extrusion molding, and special shape extrusion molding), vacuum molding, blow molding, foaming, injection press moldinGoodas injection molding or like conventional molding means, and also can be molded into a resin plate of two- or three-layered structure using a coextruding kneader.
The thus-obtained flame-retardant resin composition and flame-retardant resin moldings of the invention can be used in various industrial fields such as electrical, electronic or telecommunication, agriculture, forestry, fishery, mining, construction, foods, fibers, clothings, medical services, coal, petroleum, rubber, leathers, automobiles, precision machinery, timber, furniture, printing, musical instruments and the like.
Stated more specifically, the flame-retardant resin composition and flame-retardant resin moldings of the invention can be used for business or office automation equipment such as printers, personal computers, word processors, keyboards, PDA (personal digital assistants), telephones, facsimile machines, copying machines, ECR (electronic cash registers), desk-top electronic calculators, electronic databooks, electronic dictionaries, cards, holders and stationery; electrical household appliances and electrical equipment such as washing machines, refrigerators, cleaners, microwave ovens, lighting equipment, game machines, irons and kotatsu (low, covered table with a heat source underneath); audio-visual equipment such as TV sets, VTR, video cameras, radio casette recorders, tape recorders, mini discs, CD players, MD players, speakers and liquid crystal displays; and electric or electronic parts and telecommunication equipment such as connectors, relays, condensers, switches, printed circuit boards, coil bobbins, semiconductor sealing materials, electric wires, cables, transformers, deflecting yokes, distribution boards and clocks.
Further the flame-retardant resin composition and flame-retardant resin moldings of the invention can be widely used in the following applications: materials for automobiles, vehicles, ships, aircraft and construction such as seats (e.g. paddings, outer materials, etc.), belts, ceiling coverings, convertible tops, arm rests, door trims, rear package trays, carpets, mats, sun visors, wheel covers, mattress covers, air bags, insulation materials, hangers, hand straps, electric wire coating materials, electrical insulating materials, paints, coating materials, overlaying materials, floor materials, corner walls, deck panels, covers, plywood, ceiling boards, partition plates, side walls, carpets, wall papers, wall decorating materials, exterior decorating materials, interior decorating materials, roofing materials, sound insulating materials, thermal insulation panels and window materials; and living necessities and sportinGoodoods such as clothing, curtains, sheets, plywood, laminated fiber boards, carpets, entrance mats, seats, buckets, hoses, containers, glasses, bags, cases, goGoodles, skies, rackets, tents and musical instruments.